Abstract
Ultra micro-indentation tests on Ni and Cu samples showed increasing hardness with decreasing penetration depth over a range from 200 to 2000 nm. The results suggest increased strain hardening with decreased indentation depth. To establish that this is a real material effect, a series of tests were conducted on amorphous materials, for which strain hardening is not expected. The hardness of Metglas® was found to be independent of depth. A simple model of the dislocation densities produced under the indenter tip describes the data well. The model is based on the fact that the high density of dislocations expected under a shallow indentation would cause an increase in measured hardness. At large depths, the density of geometrically necessary dislocations is sufficiently small to have little effect on hardness, and me measured hardness approaches the intrinsic hardness of the material.
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Acknowledgments
The authors would like to acknowledge NIST and the Metglas Products division of Allied Signal Inc. for providing us with the samples used in this study. We also thank Paul Davies, Bob McDonald, and Shefford Baker for their technical guidance, and Eleanor Foskett, Bertha Jones, and Regina Campbell for their assistance in sample preparation.
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De Guzman, M.S., Neubauer, G., Flinn, P. et al. The Role of Indentation Depth on the Measured Hardness of Materials. MRS Online Proceedings Library 308, 613–618 (1993). https://doi.org/10.1557/PROC-308-613
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DOI: https://doi.org/10.1557/PROC-308-613